1. Field of the Invention
The present invention relates to an image-shake compensation apparatus for compensating for an image shake caused by a shake of hands or for some reason, in a camera or an optical unit.
2. Description of the Related Art
Since current cameras have been automated in their important operations for taking pictures, such as decisions of exposure and focusing, even persons who are unfamiliar with camera operations are unlikely to fail to take pictures.
In recent years, research has been conducted on systems for preventing shaking of hands applied to the camera from adversely affecting picture taking performance, and there are almost no causes for failure in taking pictures.
A system for preventing shaking of hands applied to the camera from adversely affecting picture taking will be briefly described below.
Shaking of hands applied to the camera when a picture is taken usually provides a vibration having a frequency of 1 to 10 Hz. To allow a picture having no image shaking to be taken even if shaking of hands is applied to the camera when the shutter is released, it is necessary to detect a value for the shaking of the camera caused by the shaking of hands and to displace a compensation lens according to the detected value. Therefore, to take a picture having no image shaking even if a shaking of the camera happens, first the camera shaking needs to be detected correctly and secondly a change in the optical axis caused by a shaking of hands needs to be compensated for.
Such a vibration (a shaking of a camera) can be detected, in principle, by mounting on the camera a shake detecting sensor for detecting acceleration, angular acceleration, angular velocity, or angular displacement, and a vibration detecting unit equipped with a calculation section for applying calculation processing to the output of the shake detecting sensor to compensate for the shaking of the camera. A compensation unit for shifting the optical axis for taking pictures is driven to suppress an image shake according to the detected information.
A vibration preventing system having a vibration detecting unit, a compensation unit, and a driving unit for driving the compensation unit has been disclosed in detail in Japanese Unexamined Patent Publication No. Hei-2-58037. Outlines of the system will be described below by referring to FIGS. 35A and 35B.
FIG. 35A is a perspective view of a compact camera having a vibration preventing system. There is shown a camera cover 61 and an imaging lens 62 of the camera, which is protected by a lens barrier when a picture is not taken (the lens barrier cannot be seen in FIG. 35A because it is retracted for taking pictures). In FIG. 35A, a main switch 63 of the camera is set such that the vibration preventing system is turned on and a picture is ready to be taken. When the main switch 63 is set to a mark OFF, a picture cannot be taken. When the main switch 63 is set to a position 64 which indicates a sports mode (high-speed shutter mode) or to a position 65 which indicates a strobe mode, the vibration preventing system is turned off and a picture can be taken (this is because the vibration preventing system is not required for these modes). When a release button 66 is pressed down, the camera performs light measurement and distance measurement, performs focusing, and then starts shake compensation. Film is exposed. A strobe flash section 67 automatically flashes light when an object is dark, or forcedly flashes light. There is also shown a viewfinder optical system 75 and an eye 76 of the user who is looking through the viewfinder.
FIG. 35B is a perspective view of the inside of the camera shown in FIG. 35A. There is shown a camera body 70, compensation means 68 for driving a compensation optical system 69 freely in X and Y directions shown in the figure to perform shake compensation, and shake detecting sensors 71p and 71y for detecting a shake in a pitch direction 72p and in a yaw direction 72y, respectively. The lens barrier 73, described above, opens and shuts in synchronization with a knob 74. The knob 74 is disposed adjacently to the main switch 63 as shown in FIG. 35A and is pushed to open the lens barrier 73 when the main switch 63 is operated. When the lens barrier 73 is shut, the compensation means 68 (more specifically, a support frame that supports the compensation optical system 69) is mechanically locked to prevent the compensation means 68 from breaking while a picture is not taken, such as while the camera is being carried.
The compensation means 68 shown in FIG. 35B is electromechanically driven with a relationship between a magnet and a coil constituting driving means to perform shake compensation. If the coil is broken due to an external impact or the magnet is damaged, the compensation means 68 cannot be driven. If external foreign matter is attached to the compensation means 68 and its movement is not smooth, successful shake compensation cannot be performed.
In such a case, it is necessary to notify the user in order to have the camera repaired soon since driving for shake compensation cannot be performed. This is especially important for the compact camera, in which the viewfinder optical system 75 is independently provided from an imaging optical system, as shown in FIG. 35A, because it is unclear whether a shake occurs or not even if the user looks through the viewfinder.
Conventional optical units such as cameras cannot detect erroneous operations of compensation units and driving units without impairing their compactness. In other words, erroneous operation of the compensation unit and the driving unit can be detected by providing a position detecting sensor, for example, and by monitoring the output of the position detecting sensor, but the size of the camera and its cost increase, which is not desired.